1. Field of the Invention
The present invention is directed to methods and apparatuses for driving fluids in a fuel cell, and more particularly, to methods and apparatuses for moving fluids, specifically water, fuel, a fuel mixture and liquid effluent, in a direct methanol fuel cell system using self-generated pressure differentials.
2. Background of the Prior Art
Substantial research has been dedicated to development of direct oxidation fuel cell systems, including but not limited to direct methanol fuel cell systems for use in portable electronics in recent years. Those skilled in the art will recognize a direct oxidation fuel cell is one that does not require fuel to be processed following its introduction into the fuel cell system. For a direct methanol fuel cell system to operate properly, it is inperative that the fluids in the system are available to the fuel cell for the generation of electricity.
Currently, direct oxidation fuel cell systems, including direct methanol fuel cell systems (DMFC Systems) are typically operated in a particular physical orientation in order for the system to properly operate (e.g., fuel supply, water supply). However, because many potential applications for DMFC Systems are operated in a variety of orientations, it is imperative that the DMFC System be able to operate regardless of its orientation.
Previous methods of supplying fuel to a fuel cell have focused on directing the fuel with a pump or series of pumps, as shown in FIG. 1. Alternatively, pressurized fuel tanks or cartridges may be used to drive fuel into the system. However, pumps result in parasitic power loss, and fabrication of pressurized fuel tanks that will effectively deliver fuel to a direct methanol fuel cell (DMFC) is cost prohibitive and difficult. In addition, in a DMFC System that recirculates the unreacted methanol/water fuel mixture and adds neat methanol to provide adequate fuel to the system, it is necessary to ensure that the new methanol is evenly mixed in the mixture prior to introduction into the anode.
It is therefore desirable to have a fuel delivery and mixture maintaining system that does not require that a pump or other power consuming device be used to manage fluid flow and composition within the fuel cell system.
The present invention provides unique methods and apparatuses for driving fluids throughout a fuel cell system, and for mixing fuel and water into a fuel mixture using pressure differentials produced by an effluent gas. Thus, the present invention allows for the movement and mixing of fluids in a direct oxidation fuel cell system without the use of electrically driven pumps or other electrically driven apparatuses.
The present invention presents novel apparatuses and methods to utilize anodically generated CO2 to maintain and provide a sufficient flow of methanol and water ultimately to the anode chamber of a fuel cell. It will be understood by those skilled in the art that the invention can be used with a variety of fuel cell configurations, including but not limited to configurations utilizing a bipolar stack, as well as those that use multiple Protonically Conductive
Membranes assembled in a single plane, or single-cell Direct Methanol Fuel Cell System designs.
Accordingly, it is an object of the present invention to provide a means to ensure that a consistent supply of the fuel mixture is provided to an anode chamber of a fuel cell to enable electricity generating reactions to continue
It is also an object of the present invention to provide orientation independence for a fuel cell system. That is, the present invention allows a fuel cell system to operate in any variety of orientations. In prior art direct oxidation fuel cell systems, the fuel cell is typically required to remain in a single position, so that gravity is used to aid in movement of liquids/gases in the system. Accordingly, the present invention allows for direct oxidation fuel cell systems to be used in portable electronics.
It is yet a further object of the present invention to provide a fuel cell system to ensure that proper amounts of the constituents that comprise the fuel mixture are supplied to a mixing chamber.
It is another object of the present invention to ensure that proper flow of the fuel mixture, liquid anode effluent comprised of unreacted fuel and water, added fuel and/or added water, occurs. Moreover, the present invention allows for the accelerated and enhanced mixing of xe2x80x9cneatxe2x80x9d methanol withxe2x80x94the liquid anode effluent and cathodically generated water.
In each of the embodiments of the invention, it is important to note that the fuel may be delivered to the system via a cartridge (similar to that used in a fountain pen) or through a tank that may be refilled. It should be further understood that the valves described in the present invention are preferably electrically actuated and allow the flow of fluid only when open, and preferably only in one direction.
Accordingly, in a first aspect of the present invention, a fuel cell system includes a housing defining an anode chamber and a cathode chamber and includes a catalyst, a protonically conductive (but electronically non-conductive) membrane positioned between the anode chamber and the cathode chamber and a first vent connecting said anode chamber with the ambient environment. The catalyst is preferably applied to the anode and cathode faces of the protonically conductive membrane. The system also includes a fuel chamber in gaseous communication with the anode chamber via a first valve, a water chamber in gaseous communication with the anode chamber via a second valve, and a mixing chamber having a second vent. The mixing chamber is in gaseous communication with the anode chamber via a third valve and receives fuel from the fuel chamber through a fuel valve, water from said water chamber via a water valve, and liquid effluent from the anode chamber via a liquid effluent valve. The mixing chamber also provides a fuel mixture to the anode chamber via a fuel mixture valve.
In yet another aspect of the present invention, a method for moving a liquid between chambers of a fuel cell system includes sealing off an anode chamber and a first chamber having a liquid stored therein of a fuel cell system from external pressure creating a closed sub-system, while allowing an effluent gas produced in the anode chamber to freely flow between the anode chamber and the first chamber, and storing a portion of said effluent gas in the first chamber. A first pressure of the sub-system increases due to an increasing volume of effluent gas being producedxe2x80x94in the anode chamber. The method also includes sealing off in the first chamber from the anode chamber, substantially ceasing the flow of the effluent gas between the anode chamber and the first chamber, creating a pressure differential between a second chamber and the first chamber by lowering a second pressure in the second chamber to a point below the first pressure, opening a conduit between the first chamber and the second chamber, where, as a result of the pressure differential, the liquid stored in the first chamber flows into the second chamber via the second conduit.
In the above aspect, the first and second chambers may be the following:
In yet another aspect of the present invention, a method for agitating a liquid stored in a first chamber of a fuel cell system includes sealing off the anode chamber from external pressure, storing an effluent gas produced in the anode chamber within the anode chamber, where pressure within the anode chamber increases over a period of time due to an increasing volume of effluent gas being produced. The method also includes creating a pressure differential between the first chamber and the anode chamber by lowering a first pressure of a first chamber to a point below the anode pressure, and opening a conduit between the anode chamber and the first chamber. As a result of the pressure differential, effluent gas stored in the anode chamber flows into the first chamber agitating the liquid stored there and is then vented to the ambient environment.
The following additional aspects of the present invention, working in conjunction with the fuel cell system described in the first aspect, are directed to methods for moving particular fluids between chambers of the fuel cell system, and are each set out below:
A method for moving a fuel and water mixture stored within the mixing chamber to the anode chamber. This method includes closing the first vent, the second vent, the first valve, the second valve, the fuel valve, the fuel mixture valve, the water valve, and the liquid effluent valve, establishing a closed sub-system between the anode chamber and the mixing chamber. The method also includes the steps of opening the third valve allowing an effluent gas produced in the anode chamber to freely flow between the anode chamber and the mixing chamber, and storing a portion of the effluent gas produced in the anode chamber in the mixing chamber. A volume of the effluent gas establishes a first pressure within the closed sub-system and the first pressure becomes increasingly higher as the effluent gas is produced. The method further includes the steps of closing the third valve to isolate the mixing chamber from the anode chamber, opening the first vent to release the first pressure in the anode chamber such that a second pressure is established within the anode chamber lower than the first pressure creating a pressure differential between the mixing chamber and the anode chamber, closing the first vent, and opening the fuel mixture valve and allowing the fuel mixture to flow from the mixing chamber into the anode chamber as a result of the pressure differential.
A method for moving water stored within the water chamber to the mixing chamber. The method includes closing the first vent, the second vent, the first valve, the third valve, the fuel valve, the fuel mixture valve, the water valve, and the liquid effluent valve, wherein a closed sub-system is established between the anode chamber and the water chamber. The method also includes the steps of opening the second valve allowing an effluent gas produced in the anode chamber to freely flow between the anode chamber and the water chamber, and storing a portion of the effluent gas produced in the anode chamber in the water chamber. A volume of the effluent gas establishes a first pressure within the closed sub-system, and the first pressure becomes increasingly higher as the effluent gas is produced. The second valve is then closed to isolate the water chamber from the anode chamber, and then the second vent is opened to lower a second pressure in the mixing chamber below the first pressure creating a pressure differential between the water chamber and the mixing chamber. The method further includes the steps of closing the second vent, opening the water valve and allowing water to flow from the water chamber into the mixing chamber as a result of the pressure differential.
A method for moving fuel stored within the fuel chamber to the mixing chamber includes closing the first vent, the second vent, the second valve, the third valve, the fuel valve, the fuel mixture valve, the water valve, and the liquid effluent valve, establishing a closed sub-system between the anode chamber and the water chamber, opening the first valve allowing an effluent gas produced in the anode chamber to freely flow between the anode chamber and the fuel chamber and storing a portion of the effluent gas produced in the anode chamber in the fuel chamber. A volume of the effluent gas establishes a first pressure within the closed sub-system which becomes increasingly higher as the effluent gas is produced. The method further includes the steps of closing the first valve to isolate the fuel chamber from the anode chamber, opening the second vent to lower a second pressure below the first pressure, creating a pressure differential between the fuel chamber and the mixing chamber, closing the second vent, opening the fuel valve and allowing fuel to flow from the fuel chamber into the mixing chamber as a result of the pressure differential.
A method for moving liquid effluent from the anode chamber to the mixing chamber includes closing the first vent, the second vent, the first valve, the second valve, the third valve, the fuel valve, the fuel mixture valve, the water valve, and the liquid effluent valve establishing a closed sub-system between the anode chamber and the liquid chamber, and storing an effluent gas produced in the anode chamber in the anode chamber. A volume of the effluent gas establishes a first pressure within the anode chamber that becomes increasingly higher as the effluent gas is produced. The method further includes opening the second vent and the effluent valve allowing an effluent liquid stored in the anode chamber to flow from the anode chamber into the mixing chamber as a result of the pressure differential.
A method for agitating a fuel mixture stored within the mixing chamber includes closing the first vent, the second vent, the first valve, the second valve, the third valve, the fuel valve, the fuel mixture valve, the water valve, and the liquid effluent valve, wherein a closed sub-system is established between the anode chamber and the water chamber, and storing an effluent gas produced in the anode chamber in the anode chamber. A volume of the effluent gas establishes a first pressure within the anode chamber that becomes increasingly higher as the effluent gas is produced. The method further includes the steps of opening the second vent and the third valve allowing the stored effluent gas to flow from the anode chamber into the mixing chamber and out the second vent, where the fuel mixture stored in the mixing chamber is agitated as a result of the effluent gas flowing into the mixing chamber and out of the second vent as a result of the pressure differential.
In the preceding aspects, pressure may be lowered in a particular chamber by venting the respective chamber to an environment having a lower pressure. Thus, such an environment may include ambient air pressure.
In yet another aspect of the present invention, a fuel cell system similar to the first aspect includes a pump in place of the mixing chamber. Effluent gas is used to move fuel from the fuel chamber to the pump. Thus, this aspect includes a housing defining an anode chamber and a cathode chamber and including a catalyst and a protonically conductive, but electronically non-conductive, membrane positioned between the anode chamber and the cathode chamber where the anode chamber includes a first vent, a fuel chamber in gaseous communication with the anode chamber via a first valve, a water chamber, and a pump. The pump receives fuel from the fuel chamber via a fuel valve, water from the water chamber, and liquid effluent from the anode chamber. The pump provides a fuel mixture to the anode chamber.
In yet a further aspect of the present invention, the above fuel cell system is used with a method for supplying fuel to the pump and includes closing the fuel valve, opening the first valve allowing an effluent gas produced in the anode chamber to freely flow between the anode chamber and the fuel chamber, establishing a closed sub-system between the anode chamber and the fuel chamber, and storing a portion of said effluent gas produced in the anode chamber in the fuel chamber. A volume of the effluent gas establishes a first pressure within the closed sub-system, with the first pressure becoming increasingly higher as the effluent gas is produced and the first pressure is higher than a second pressure of the pump establishing a pressure differential there between. The method also includes closing the first valve to isolate the fuel chamber from the anode chamber, opening the fuel valve and allowing fuel to flow from the fuel chamber into the pump as a result of the pressure differential.
In yet a further aspect of the present invention, a fuel cell system includes a housing defining an anode chamber and a cathode chamber and including a catalyst, a protonically conductive but electronically non-conductive membrane positioned between the anode chamber and the cathode chamber and a first vent, a first conduit having a first end for receiving liquid effluent from the anode chamber and a second end for supplying a fuel mixture comprised of fuel and/or water, and the liquid effluent to the anode chamber, and a fuel chamber in gaseous communication with the anode chamber via a first valve and in communication with the first conduit via a fuel valve. The water chamber may also be in communication with the cathode chamber to receive cathodically generated water within the cathode chamber.
In yet another aspect of the present invention, a method for controlling a concentration of fuel in a fuel-water mixture for a direct oxidation fuel cell system includes determining a first concentration level of fuel in a fuel-water mixture of an anode chamber of a direct oxidation fuel cell system and comparing the first concentration level to a second required concentration level required for a particular operating condition. Fuel is added to the fuel-water mixture when the first concentration level is less than the second required concentration level, under given operating conditions and water is added to the fuel-water mixture when the first concentration level is higher than the second required concentration level under given operating conditions.
In a related aspect, a system for performing this method includes a housing defining an anode chamber and a cathode chamber, with the housing also including a catalyst and a protonically conductive but electronically non-conductive membrane and the anode chamber including a fuel-water mixture. The system also includes a fuel concentration sensor for determining a first concentration level of fuel in said fuel-water mixture, a fuel chamber for storage of fuel, where the fuel chamber is in communication with the liquid-fuel mixture, a water chamber for storage of water, where the water chamber is in communication with the fuel-water mixture, and a controller for controlling a first flow of fuel to the fuel-water mixture, for controlling a second flow of water to the fuel-water mixture, and including a memory having a look-up table stored therein. The look-up table includes operating condition data and associated fuel concentration levels.
For a better understanding of the above aspects of the invention, reference is made to the below referenced drawings and written description following immediately thereafter